What is SEO in website design?

SEO in website design means building the site itself, the structure, speed, code, and layout, so search engines can find, understand, and rank it. It's built into the foundation, not added on after launch.

This is different from ongoing SEO work like content and link building. A well-designed site gives that later work something solid to build on. A poorly built one fights against it no matter how much content gets added.